Momentum-conserving wind-driven electrical generator

ABSTRACT

Wind-driven electrical generators will slow and lose kinetic energy when the wind slows or stops. When the wind slows or stops, kinetic energy in the rotating turbine and other rotating components that would otherwise be lost, is conserved by supplying a supplemental mechanical energy to the rotating components using a battery-powered motor. The electrical power for the drive motor is obtained from solar-charged batteries. In an alternate embodiment, solar cells provide all of the energy for the drive motor.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/019,893, filed Jan. 25, 2008. This applicationtherefore claims the benefit of the filing date of U.S. patentapplication Ser. No. 12/019,893.

BACKGROUND OF THE INVENTION

FIG. 1 is a simplified depiction of a wind-driven generator 2. Wind,represented by reference numeral 3, causes a propeller 4 to rotate. Thepropeller 4 drives a generator 5, which generates electricity. Theelectricity generated by the generator 5 flows through a transmissionline 6 to a load, such as an electrical power grid represented byreference numeral 7 or a consumer's home, a business or a small factory.

A problem with wind-driven electric power generation is that wind isunreliable and its speed is never constant. Excess propeller speedcaused by high winds can be limited by a brake or by blade pitch,however, propeller speed cannot be downwardly controlled when windvelocity falls. When the wind speed falls, electric output power willfall since electric output power is directly related to propellerrotation speed. When the wind stops, output power will also stop.Fluctuating wind speed will therefore cause generator output tofluctuate.

A closely related problem is that the propeller 4 requires a certainamount of kinetic energy, i.e., rotational velocity, before it can evenbegin to generate usable amounts of output power, as FIG. 2 shows. Someenergy must be imparted to the propeller before it can generate usableelectric output power. When the wind slows or stops, latent kineticenergy in the rotating propeller and other rotation machinery connectedto the propeller begins to dissipate through wind loss, bearing loss andelectrical loading, if the generator is not disconnected from itselectrical load. The lost kinetic energy must be restored by the windbefore the generator can resume generating power. Maintaining propellerspeed when the wind slows or stops might improve wind generatorefficiency by shortening the time required to bring the generatoron-line after the wind speed has recovered. A method and apparatus forsimply and economically maintaining propeller speed, during intervalswhen the wind slows or has stopped, would be an advantage over the priorart.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified depiction of a wind-driven generator 2.

FIG. 2 is a graph of wind generator output power as a function of windspeed;

FIG. 3 is a schematic diagram of a momentum-conserving wind-driven,momentum-conserving electricity generator;

FIG. 4 is a schematic diagram of an alternate embodiment of amomentum-conserving wind-driven, momentum-conserving electricitygenerator;

FIG. 5 is a schematic diagram of yet another embodiment of amomentum-conserving wind-driven, momentum-conserving electricitygenerator;

FIG. 6 depicts a wind driven generator having solar cells on the towersupporting the wind driven generator;

FIGS. 7A and 7B depict different positions of a propeller blade rotatedabout its lengthwise axis;

FIG. 8 depicts where the views shown in FIGS. 7A and 7B are taken.

DETAILED DESCRIPTION

FIG. 3 is a schematic diagram of a momentum-conserving wind-drivenelectricity generator 10. The generator 10 is comprised of awind-driven, rotating propeller 12 that is mounted to a first elongateddrive shaft 16. The propeller 12 is comprised of two or more propellerblades 14 that are affixed to a central hub 36 that houses abi-directional servo motor (not shown) for each blade. Each servo motoris coupled to the controller 34 and rotates the blade 14 around itslongitudinal axes (extending outwardly, radial to the hub but not shownfor clarity) in order to control the blade's pitch under softwarecontrol. The ability to controllably rotate the propeller blades aroundtheir longitudinal axes provides an ability to control blade speed inresponse to wind speed fluctuations.

When the wind velocity is too low to generate usable power and/or whenthe wind has stopped, propeller momentum and the momentum or otherrotating machinery connected to the propeller is conserved, at leasttemporarily, using electric energy stored in rechargeable batteries todrive a motor that keeps the propeller turning. The rechargeablebatteries are kept charged using energy from photovoltaic cells or fromthe generator 10 itself during periods when wind velocity permits thegenerator 12 to produce excess power. In an alternate embodiment, theback-up drive motor is powered directly and exclusively by energyprovided by arrays of photovoltaic cells, i.e., solar cells.

Still referring to FIG. 3, wind 4 that strike the blades 14 of thepropeller 12 will undergo a change in momentum and impart a forceagainst the propeller blade 14 that causes the propeller 12 to rotateabout its axis, which is the geometric center of the first drive shaft16. Stated another way, when the wind 4 blows, it will cause thepropeller 12 to rotate the first drive shaft 16, to which the propeller12 is attached.

The first drive shaft 16 is mechanically coupled to a first drive gear18, which includes a magnet, which in combination with a Hall-effectsensor, is used to measure first drive gear 18 rotation speed. The firstdrive gear 18 is engaged to a much smaller-diameter second driven gear20 so that the relatively slow propeller 12 speed produces a higherdriven gear 20 rotation speed.

Driven gear 20, which can also include one or more magnets, is attachedto a second elongated drive shaft 22. The mechanically rotating armature23, i.e., the rotating electric field winding 23 of a generator 24, iscoupled to the second drive shaft 22 such that when the wind blows, itcauses the propeller 12 to rotate. Propeller rotation causes the firstdrive shaft 16 and the first drive gear 18 to both rotate. Rotation ofthe first drive gear causes the second driven gear 20 and the seconddrive shaft 22 to rotate, which causes the generator field winding 23 torotate, albeit in a direction, opposite the propeller, first drive shaft16 and first drive gear 18. Since the elongated drive shaft 22 isdirectly connected to rotating field winding 23 of the generator 24,propeller rotation causes the generator 24 to generate electrical energyin the electrical armature 26 of the generator 24.

Those of ordinary skill in the art are familiar with the use ofso-called Hall-effect sensors to detect the position of a rotating shaftbut also to measure shaft rotation speed. In the embodiments disclosedherein, a shaft rotation speed detector 32A, preferably embodied as aHall effect sensor, is mounted at an effective distance away frommagnets in the first gear 18. The magnets and their rotation enable thedetector 32A, in combination with the controller 34 to which thedetector 32A is coupled, to detect variations in the shaft rotationalspeed. Since the detector 32A, in combination with the controller 34, isable to detect and measure shaft speed, detector 32 is therefore able toindirectly detect wind speed as well as indirectly detect electricalloading on the generator 10 because wind speed and loading will bothaffect shaft rotation speed.

Those of ordinary skill in the art know that the rotational speed of thepropeller 12 rarely goes over a few dozen turns per minute. Thegenerator 24, however, requires a relatively high rotation speed. Thedriven gear 20 is therefore usually much smaller than the drive gear 18in order to obtain an acceptable rotation speed from a relativelyslow-turning propeller 12. The faster rotational speed of the drivengear 20 enables a Hall-effect sensor 32B located proximate to magnets inthe driven gear 20 to detect relatively small changes in the rotationalspeed of the gear 20, shaft 22 and generator 24. It will thereforeusually be advantageous to detect propeller 12 speed fluctuations usinga second Hall-effect sensor 32B proximate to the driven gear 20, since asmall change in propeller rotation speed will cause a larger change indriven gear 20 rotation speed.

As set forth above, generator 24 rotation speed will be determined byboth the wind speed and the electrical load 50 on the generator 24.Stated another way, shaft speeds will decrease as electrical loading isincreased. In an alternate embodiment, wind speed is measured by one ormore other kinds of wind speed detectors, such as one or more pitottubes 52. Shaft speed decreases, i.e., deceleration, attributable towind speed can be more accurately attributed to wind speed decreases bymeasuring wind speed using a device such as a pitot tube in combinationwith a shaft speed detector since a pitot tube will not be able todetect minute wind speed changes that might nevertheless affect shaftspeed that is detectable by the sensors 32A and/or 32B.

In the embodiment shown in FIG. 3, the elongated shaft 22 extends allthe way through the generator 24 and is directly coupled to the rotatingarmature of a D.C. drive motor 30. Stated another way, the field of thegenerator 24 and the armature of the drive motor 30 are bothmechanically coupled to the same elongated shaft 22 such that theyrotate together. Since the armature of the drive motor 30 rotates withthe elongated shaft 22, the mechanical coupling of the elongated shaft22 to the armature of the motor 30 effectively couples the drive motor30 to one or both of the detectors 32A and 32B. The detector 32A (and/or32B) can therefore be used to indirectly measure the speed of the drivemotor 30 whenever the drive motor 30 is “powered up” to providerotational torque to the elongated shaft 22.

As was stated above, when wind 4 speed drops, the rotating machinery inthe generator 10 will also drop. When the wind stops, the rotatingmachinery in the generator will also stop. When the wind speed drops orwhen the wind stops, kinetic energy in the rotating machinery, i.e.,angular momentum, can be maintained or conserved, by adding rotationaltorque from an external source, which in each of FIG. 3, FIG. 4 and FIG.5, is the D.C. powered drive motor 30. As shown in the figures and asdescribed above, drive motor 30 is mechanically connected to therotating machinery and powered up, under software control, whenever windspeed falls or when the wind stops such that usable output power cannotbe generated by the wind.

Clean and renewable electrical power is supplied to the drive motor 30from either a rechargeable battery pack 40 or a photovoltaic array,i.e., solar cells 42 or both the battery 40 and the solar cells 42together. When electrical power is applied to the drive motor 30 fromthe battery 40 and/or the solar cells 42, the drive motor 30 can atleast temporarily overcome losses in the rotating machinery in order tokeep the rotating machinery rotating at either full speed or at areduced speed until the wind speed adequately picks up. Clean andrenewable electrical energy stored in the battery 40 can therefore beused to conserve the angular momentum acquired by rotating machinery ofthe generator when wind speed is too low to drive an electrical load orwhen the wind has stopped. Maintaining the rotation of speed of at leastthe propeller, i.e., conserving its momentum, avoids having to waituntil an otherwise stopped propeller is brought back up to speed by thewind and thus makes wind-generated power available sooner, i.e., withouthaving to wait for the wind to adequately spin-up the propeller 12.

Electrical energy from the battery pack 40 and the solar cells 42 isprovided to the drive motor 30 through a software-controlled switch 38,which is activated by and under the control of a controller 34, such asa microprocessor or micro-controller. The controller 34 “closes” theswitch 38 by sending an appropriate signal to the coil 39 for the switch38, which causes the contacts of the switch to close and complete anelectrical circuit between the drive motor 30 and the rechargeablebattery 40 and solar cells 42. When the switch 38 closes, the battery 40and the solar cells 42 are connected to the motor 30. When the windspeed picks up and becomes sufficient to generate electrical power, theswitch 38 is opened by the controller 34, which disconnects the motor 30from the battery 40 and the solar cells 42. Energy required to at leasttemporarily maintain propeller 12 rotation during wind outages istherefore supplied by solar energy captured by the solar cells 42. Thebattery is also kept charged by the solar cells when they're not neededto power the drive motor 30.

In one embodiment, the solar cells 42 are attached to the pole (See FIG.6) or a tower that the generator 10 is mounted on. In yet anotherembodiment, solar cells are applied to surfaces of the propeller. Sinceit may be possible to mount numerous cells on a pole and/or tower, analternate embodiment of the generators disclosed herein include a drivemotor 30 that is powered exclusively by energy obtained from solar cells42, as well as in addition to power obtained from a battery pack 40.

The controller 34 that controls operation of the generator 10 ispreferably a microcontroller or microprocessor, both of which are wellknown to those of ordinary skill. Such devices execute programinstructions that are stored in addressable memory devices, not shownfor clarity and simplicity but well known to those of ordinary skill.

In the generator 10 shown in FIG. 3, program instructions executed bythe controller 34 cause the controller 34 to monitor the output of oneor more pitot tubes 52 as well as the Hall-effect sensor(s) 32A and/or32B. When the pitot tubes 52 and/or Hall-effect sensors 32A and/or 32Bindicate that the propeller speed is decreasing due to wind speed, thecontroller 34 executes instructions to keep the rotating machineryturning.

When a wind speed loss is detected, the controller 34 first disconnectsthe generator 10 from any electrical load 50 that it might be driving.Disconnecting the electrical load 50 is readily accomplished using asoftware controllable transfer switch or relay 64, well known to thoseof ordinary skill, the actuation of which disconnects the generator 24output from any load that it was previously driving.

Simultaneously with or shortly after load disconnection, the controller34 changes the pitch of the blades 14 of the propeller 12 in order tominimize wind drag. Reducing wind drag by “feathering” the propellerblades allows the propeller and other rotating machinery connected tothe propeller to continue to rotate longer than they would if thepropeller blades were “facing” into the air through which the propellerrotates.

In the embodiments disclosed herein, the blades 14 of the propellers 12extend radially from a central hub 36. FIGS. 7A and 7B are top views ofthe propeller 12 blade 14 and illustrate how the blade 14 can be rotatedto have different angular orientations or pitch. At least threedifferent pitches are shown and which are identified as 14-1, 14-2 and14-3. The broken line in FIG. 8 shows the direction from which the viewsin FIGS. 7A and 7B are taken.

In a first position denoted as 14-1, the planar face of the blade 14 ofthe propeller 12 forms a first angle denoted as “α” relative to the axisof the shaft 16 and which is approximately 75 degrees. In a secondposition 14-2, the blade 14 forms a second angle “β” that isapproximately 45 degrees. In a third position 14-3, the blade 14 is“flat.” When the propeller blade 14 is flat as shown in the thirdposition 14-3, wind directed at the propeller 12 will not cause thepropeller 12 to rotate but wind resistance created by the blades 14 whenthey are rotated by the motor 30, will be minimized. In other words, by“feathering” the blades 14 to the third position 14-3, the power thatmust be provided by the drive motor 30 to keep the propeller 12 rotatingwill be significantly reduced as compared to the power that would berequired when the blades are at the first position 14-1 or secondposition 14-2.

When the controller 34 detects that the shaft 16 and/or 18 is slowingdue to wind speed loss, the controller 34 sends signals to servo motorswithin the hub 36, to cause the blades to rotate to the third position14-3 (shown in FIG. 7B) so that the wind resistance created by therotation of the blades 14, and which must be overcome by the drive motor30, can be minimized. By rotating the blades 14 to minimize windresistance, the power required from the drive motor 30 to maintain thespeed of the propeller 12 and other rotating machinery connected to thepropeller is minimized.

Simultaneously with or shortly after rotating the propeller blades tominimize wind drag, the controller 34 “closes” switch 38 to connect apower source, either the battery pack 40, the solar cells 42 or both, tothe drive motor 30. Closing switch 38 therefore activates the drivemotor 30, which will apply rotational torque to the rotating machineryfor as long as the rechargeable battery pack 40 and the solar cells 42are able to keep the motor turning the rotating components of thegenerator, i.e., the generator 24, the drive shafts 22 and 16 and thepropeller 12. When the wind driving the propeller 12 dies down or stops,the momentum of the rotating propeller and of other rotating components,can be conserved for as long as the battery 40 and/or the solar cells 42are able, by having the drive motor 30 supply mechanical energy to therotating propeller. Maintaining the propeller's rotation from thebattery pack 40 and solar cells 42 will minimize the energy that must berestored to the propeller by the wind, before the generator 10 can startgenerating power again and hence reduce the time that the generator isunavailable.

FIG. 4 depicts another generator embodiment 10B. In FIG. 4, thegenerator 24 and the drive motor 30 are separately and independentlyconnectable to the driven gear 20 through a combination ofseparately-operable electrically-controlled clutches 54 and 56 anddifferential gears 58. The differential gears 58 and clutches enable thedriven gear 20 to be mechanically connected to either the generator 24or the drive motor 30. The embodiment of FIG. 4 differs from theembodiment of FIG. 3 by the mechanical disconnection of the generator 24from the shaft 22 and therefore the shaft 16 and propeller 12 and otherrotating machinery. Since the battery 40 and/or solar cells 42 are notrequired to supply power to the motor 30 that would be needed to keepthe generator 24 rotating, a battery 40 and solar cells 42 used in theembodiment depicted in FIG. 4 are able to keep the propeller 12 anddrive shafts 16 and 22 rotating longer than they would the embodimentshown in FIG. 3.

As with the embodiment shown in FIG. 3, in FIG. 4, the controller 34read signals from wind speed sensors, such as one or more pitot tubes 52and/or one or more shaft speed sensors 32A and 32B. When the controller34 detects that the wind is falling or that the wind has stopped, thecontroller 34 is programmed to send a signal to the generator clutch 54to mechanically disconnect the generator 24 from the rotating drivetrain, i.e., driven gear 20 and shaft 22. Simultaneously or shortlythereafter, the controller sends a different signal to the motor clutch56, which mechanically connects the drive motor 30 to the driven gear20, through the differential gears 58.

After the generator 24 has been mechanically disconnected from the drivegear 20 and after the drive motor 30 has been connected in its place,the controller sends a third signal to a solenoid 38, which in FIG. 4 isconfigured to connect the drive motor 30 to the rechargeable batterypack 40 and the solar cells 42 in order to energize the drive motor 30.

As with the embodiment depicted in FIG. 3, the rechargeable battery pack40 is kept in a charged state using current supplied to it by one ormore photovoltaic solar cells 42. As with the embodiment depicted inFIG. 3, power for the drive motor 30 can also be provided to it by thesolar cells 42, either in parallel with the battery pack 40 orexclusively, at the same time that the battery pack 40 provides power tothe motor 30.

The generator clutch 54 and the drive motor clutch 56 areelectrically-actuated clutches that can be separately and independentlycontrolled by separate and corresponding solenoids, which are not shownfor clarity. In an alternate embodiment, a single double-pole,double-throw solenoid could be used to control both clutches by a singlesignal from the controller 34. The generator clutch 54 and/or the drivemotor clutch 56 can also be either pneumatic or hydraulic, with theapplication of the working fluid, i.e., compressed air or hydraulicfluid, determined by the actuation of appropriate, software-controlledvalves, which are also not shown for clarity.

Referring now to FIG. 5 there is shown yet another embodiment 10C, of amomentum-conserving wind-driven electricity generator 10. In FIG. 5, aD.C. motor/D.C. generator 60 is used in place of a separate motor andseparate generator.

In a first mode of operation, the motor/generator 60 armature (notshown) is configured to operate as a D.C. generator. An external D.C.source generates a magnetic field in that rotates within field windingsthat are coupled to an electrical load. Rotation of the “armature” bythe shaft 22 causes the motor/generator 60 to generate, i.e., outputelectric power to an electrical load.

In a second mode of operation, the electrical connections themotor/generator 44 are reversed from what they are in the first mode. Inthe second mode, the motor/generator operates as a D.C. motor. In thesecond mode, the motor/generator 44 is electrically disconnected fromthe electrical load using a transfer switch, the actuation of whichconnects the stationary “field” windings to the rechargeable batterypack 40 and/or the solar cells 42. As with the first and secondembodiments, the D.C. motor in the third embodiment can be powered bythe battery or the solar cells or both the battery and the solar cellsin parallel.

In FIG. 5, electrically re-configuring the motor/generator 60 tofunction as either a generator or a drive motor eliminates the need forclutches and gears required by the embodiment shown in FIG. 4. Theembodiment of FIG. 5 also obviates the need to keep two machinesrotating as required by the embodiment shown in FIG. 3. By simplyre-configuring the motor/generator 60 based on wind conditions, themomentum of the rotating propeller 12 can be conserved so that the whenwind conditions permit electricity generation to resume, all that needsto be done is to switch the transfer switch 52 from one position toanother.

Those of ordinary skill in the art will appreciate and recognize thatthe true scope of the invention is defined by the appurtenant claims andnot by the foregoing description.

1. In a wind-driven electrical generator comprised of a propellercoupled to a drive shaft, the propeller being comprised of a pluralityof blades affixed to a central hub that rotates with the drive shaft andwhich houses at least one servo motor, the at least one servo motorbeing coupled to a controller and configured to rotate at least onepropeller blade around an axis of the propeller blade that extendsoutwardly from the central hub, the at least one servo motor controllingthe blade's pitch, a method of controlling the propeller comprising thesteps of: detecting a drive shaft deceleration; sending a first signalto the at least one servo motor, responsive to a detected drive shaftdeceleration, the first signal causing the at least one servo motor tochange the pitch of at least one of the plurality of propeller blades toreduce wind drag on the propeller; sending a second signal to at leastone switch, responsive to a detected drive shaft deceleration, thesecond signal causing the switch to reconfigure the generator to act asa motor, the motor functioning to maintain propeller rotation.
 2. Themethod of claim 1, further including the step of electricallyde-coupling the generator from an electrical load, prior to the step ofsending a first signal.
 3. The method of claim 1, wherein the driveshaft of the wind-driven electrical generator is mechanically coupled toan electricity generator wherein, said electricity generator is capableof being reconfigured to operate as a motor to rotate the propeller.